The invention relates to a conditional access system and, more particularly, to a descrambling device intended to be compatible with several conditional access sub-systems. Such a device can be included, for example, in a pay-TV decoder.
A conditional access sub-system (CASS) is an access control code (software part) that controls a descrambling circuit (hardware part).
A CASS carries out different functions such as, for example, the processing of the Entitlement Control Messages (ECM) that contain the ciphered descrambling keys and the processing of the Entitlement Management Messages (EMM) that contain the users entitlements.
In many cases, a pay-TV decoder contains a single CASS specific, for example, to a Network Operator.
In other cases, pay-TV decoders have to allow the use of different CASS. Then, such decoders use a standard DVB-CI interface. A standard DVB-CI interface is a PCMCIA module that contains one CASS.
The decoder itself may no more contain any conditional access part. When a TV viewer wants to use a specific CASS, he must take the right DVB-CI interface module and plug it into the decoder.
Such a system is expensive (there is a cost for each DVB-CI interface module), not ergonomic (many manipulations are required to use several conditional access sub-systems) and rather slow (a dialog is necessary between the DVB-CI interface module and the decoder).
The invention does not have these drawbacks.
The invention concerns a descrambling device comprising hardware resources and first memory zones to store at least two different access control codes for controlling the hardware resources. The hardware resources are shared between the different access control codes thanks to an arbitration code stored in a CASS supervisor module.
The invention concerns also a method for descrambling scrambled data by means of an access control code controlling hardware resources. The method comprises a step to allow at least one other access control code to control the hardware resources through an arbitration code.
According to an improvement of the invention, access control codes can be downloaded in the first memory zones by means of a loader contained in the device.